The phrase ‘suffering from a silent cold heart’ is a metaphor for a situation where someone silently endures pain or sadness without being able to express it.
Here, ‘Neunggasum’ refers to deep, frustrating emotional pain or a lump in the throat that cannot be revealed outwardly, as if it has become cold and hardened.
In other words, it is a concise term that describes a state of suffering due to being unable to express one’s difficult circumstances or painful emotions externally, keeping them bottled up inside one’s heart.